Rheostat switch



March 11, 1958 w. B. DULL 2,826,663

RHEOSTAT SWITCH Filed June 9, 1954 United States Patent RHEOSTAT SWITCH William B. Dull, Coldwater, Mich., assignor to Kingston Products Corporation, Bronson, Mich., a corporation Application June 9, 1954, Serial No. 435,403

3 Claims. (Cl. 201-48) within an enclosure and carrying and supporting the rotatable actuating parts of the switch.

The principles of the present invention find a particularly useful application when embodied in a rheostat switch construction, by way of illustrative example, a rheostat switch construction which may be adapted for automotive use and which may be carried on the dashboard of an automotive vehicle so as to be finger manipulable by the automobile operator or an automobile passenger.

With the switch apparatus and particularly with a rheostat switch, thermal energy is generated with the result that thermally conductive portions of the switch assembly become heated to an elevated temperature.

For example, in one form of rheostat switch apparatus utilized for controlling the blower motors of an automotive air conditioner installation, so much heat was generated that the finger manipulable portions of the switch assembly were uncomfortable to touch, thereby interfering with the proper operation of the switch assembly.

In attempting to overcome such problem, efforts were made to ventilate the switch, thereby maximizing the dis- .sipation of thermal energy likely to be conducted by the thermally conductive portions of the switch apparatus.

Efforts were also made to reduce the number of components of the switch assembly and with particular regard to the possibility of reducing the number of thermally conductive components of the switch assembly.

Under some circumstances, however, it is highly desirable that the actual finger manipulable actuating member of the switch be made of a metal material decoratively enhanced by chrome or nickel plating, a form of material having good thermal conductivity characteristics and having the effect, therefore, of offsetting the objectives of the enumerated proposals for the provision of an improved switch structure.

In accordance with the principles of the present invention, there is provided an improved switch assembly which not only utilizes a reduced number of highly simplified components but also a switch assembly which utilizes an actuating member consisting of a rigid synthetic resin having thermal and electrical insulative properties and which affords a design flexibility permitting the use of chrome or nickel plated actuating knobs.

These objectives are attained in accordance with the principles of the present invention by providing a switch construction utilizing a sheet form member bent to provide a centrally apertured radially extending wall having circumferentially spaced longitudinal tongues. A base assembly is carried by the tongues in spaced relation to the wall, thereby to form an enclosure. Rotatably ac tuatable switch means are provided in the housing and may take the form of an arcuately shaped helically wound coil forming a rheostat resistance. An angularly adjustable rotatable actuator member is provided within the enclosure and engages the coil as well as a contact terminal carried by the base assembly.

To adjust the actuating member and to carry the actuating member rotatably within the enclosure, there is provided a rigid synthetic resin shaft, the shaft being made of a material having favorable thermal and electrical insulative properties such as molded nylon or the like. At one end of the shaft inside of the enclosure there is provided an enlarged radially extending portion for carrying the actuating member. The shaft projects through and is rotatably journaled in the centrally apertured radially extending wall so that the opposite end of the shaft extends into a manually accessible location spaced away from the enclosure. A suitable actuating knob may be fastened to the free end of the shaft, which knob may be conveniently made from a metal decoratively enhanced by chrome or nickel plating, however, the knob will be electrically and thermally insulated by virtue of the nylon shaft. Furthermore, the radially extending wall may be provided with means having a metallic hearing surface so that the nylon shaft will be journaled and virtually self-lubricated, it being appreciated that nylon engaging with metal exhibits favorable anti-friction characteristics.

It is an object of the present invention, therefore, to provide an improved switch construction utilizing a reduced number of simplified parts which are convenient and economical to fabricate and which are completely reliable and rugged in use.

Another object of the present invention is to provide a switch construction having a shaft actuator consisting of a rigid synthetic resin having thermal and electrical insulative properties.

A further object of the present invention is to provide a rheostat switch which is manually actuatable and wherein the finger manipulatable portions thereof will not be heated to an elevated temperature even if made from material having high thermal conductivity.

A still further object of the present invention is to provide a switch construction wherein a movable contact carrier and a rotatable actuating shaft therefor are integrally made as a one piece molded synthetic resin material.

Yet another object of the present invention is to provide a switch construction wherein a rotatable switch actuator consists of an integral one piece member providing a longitudinally extending rotatable shaft for receiving a manually engageable actuating knob.

Many other features, advantages and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description which follows and the accompanying sheet of drawings in which a preferred embodiment of a switch construction embodying the principles of the present invention is shown by way of illustrative example.

On the drawings:

Figure l is an exploded view of a switch construction showing parts in elevation and showing other parts broken away and in cross-section showing the-components provided in accordance with the principles of the present invention.

Figure 2 is an elevational view of an assembled switch,

Figure 4 is an end elevational view of the actuating,

Patented Mar. 11, 1958 member provided "in-accordance with the principles "of the present invention.

Figure isan end elevational view showingthe other. end ofthe'actuatormemberof Figure' tgand v Figure "6 'is a-partial or fragmentary cross-sectional view "showing "additional"-'details of construction of the actuator member and illustrating the positioning arms biasing springthereon.

As shown'on the drawings: 7

The switch construction of the present invention is illustrated generally at 10 andcomprises a sheet form housing-member '11 bentto provide a radiallyextending walll'Z which is centrally-aperturedf-as at l3 and which has a longitudinally extending rigidi'fying peripheral flange 14. The housing member 11 -is' further'character'izecl bythe provisionofaplurality'of'circumferentiallyspaced longitudinally-extending tongues" 16; 'In "the present embodiment, there "are "three-tongues 16', each *decreasing in -size towards one =endlthereof soas'toterminate in a 'lip portion indicated by the reference numeral 17.

.A generally cylindrical andtubular =stem member 18 is :provided. The stem member '18 has =a'longitudinally extending bore 19 which provides a metallic'b'earing surface imregister 'iwith the-central aperture: 13 'of the radial wall 12;. One end -of :the stem member -18'is received within :the central' aperture and staked-portions indicated': at i9-retain the stem member 18 in 'firm "assembly with' the housing member 11. The stemmember 18 .is peripherally thread'erlxas at. 2tl tofa'cilitate mounting of thesswitchnssemblyi10sonithe dashboard ofan'automobile or upon some other mounting surface.

-A base assembly-indicated .generally at 21 comprises a disc shaped ceramim'bodyfhaving ta plurality of circumferentially- :spacedv :throughtholes L22 extending il'ongitudinally therethrough. :The ;ceramic body has opposed faces 23 and 24. Secured to theafacea23isan:annular stationarycontactzplate 26. .Thegplatelo isretainedbysa rivet2r7: extending longitudinallyzthroughttheceramic body and also serving 'to'retain atcontact' terminal28 which extends longitudinally from the face 241of -the;ceramic body.

The -.face.2-3.= of the ceramic :bodyisfurther characterized by the provision :ofan :arcuate groove.2-9 which lies in longitudinal.register'with thethrough holes 22and which receives an arcuately shapedihelically wound .-;resistance coil 30 cemented .or otherwise firmly connected ito the ceramictbody. .A contactrterminal .31 is electricallycconnected .to thee-coil. 30.

onrthe-facezft, therelis provided; a plurality-.of.circnmferentially spaced recesses 32 which receive the bentover lips .17 of the tongues 16 thereby placing-the .base in assembly with the housin member 1'1,,.the ceramic .body lying in longitudinally spaced relation relative to ,the radially extending wall '12. .Furthermore, the base assembly 21,.together-with theihousing member 11 forms an enclosure 33 "in which the switch actuatingmeans .are confined.

First of all, there is provided a :rotatable actuating member :whichxtakes tthe vform of a .contact :plate indicatedJat 34. The-:contact'plate34uis madeof electrically conductive material and has lterminal .portions 3'6 which slid-ably engage-the contact plate 26.

A second contact terminal portion 37 is provided by a peripheral embossment formed on-the plate 34 inregister with a longitudinally extending contaet face provided by 'thecoil 30, Whichtace projects longitudinally beyond the radial faceof the ceraniicbody. I

In accordance with theprinciplesof the present invention, an actuator member indicatediegfinerally .at '40 is provided, which-mcmb6r 40 consists of a rigidlsynthetic resin "having thermal and lectricalinsulative properties and. being formed toprovide a-rotatable.shaft 41 which is journaledin the bearing surface 19 and which projects 0f longitudinally ofiset lugs 44 provided on opposite sides of the contact plate 34.

As shown, in Figure 4,. the enlarged portion 42 also has an upstanding :circular boss 46'iforme'd Jon "the end face thereof and spaced concentrically"inwardly of arcu- .ately shapedsshoulders-47 sand; 43: respectively, thereby to provide a generally annular recess, 49 receiving and seating the end of-a coil spring StIinse'rted as a continuous biasing means between the contact plate 34 and the actuating member 40.

It will be appreciated that the peripheral surface of the shaft 'portion'4'1 of the'actuator member 1481s approximately the same diameter as the bearing surface provided "by' the '':bore' 19 "extending longitudinally through the stem -member 1:3. It will "be further appreciated; therefore, thatthe-enlarged"radiallyextending portion 42 onthe-end ofthe actuator member tl'is considerably larger insizethan thebore19, thereby to e'fifect a'confinement thereof :withintheenclosure 33 whenthe -housing member 11 is assembled tothe base assembly 21. The continuous biasingmeans inthe .form of the coil spring 5i therefore; has the ctfect of -loading the actuator member 40iin-onedirection-and in'loading'the contact plate 34' in a'naopposite direction 5 into springbias contact with the contact plate' ztr andtheresistance coil 30.

At the-other 'endof the-actuating member 4t ,'there is provid'ed a fiat 5 1 adapted-1o se-at-a'-set-screw 52 carried by a manually engageable actuating knob.

Since the actuating mcrn ber -40 is =-rnade of a rigid synthetic resin h-avinglthermahandelectrically insulative properties, it vwilli be appreciated that the knob 53 I may i be maderofi-ai metallic material capable: of" being decorativelycenhanced'by a=chrome or nickel plating, yet such kno'b :53 will Jbeinsulated from 'thesW-iIch mechanism bothzithermallyi andtelectrically.

The terms .insulator ia11d iconductorwwith respect to both :heat and :el'ectricityare well understood 'by those skillediinithe art, notwithstandi-ng the fact that all materials are generally considered to have at least limited heat and electrical conductiVityand no material is considered to be a perfect insulator. For *the purpose of simplification in this specification, it *will 3 be noted that heat conductors are generally considered to'have'a thermal conductivity constant fk which is defined as the quantity-of heat-(Biron. or calories) that flows ina unit :of time (one-'hour'or'one'second) through a unit area of plate (on: sqnft; or one sq.crn.-)-of unit thickness (one ft. or one cm.) 'having-unitdifference oftemperature (1 F. or '1"C;) between its faces. The thermal'conductivity of diiferent materials varies greatly. For'rnetals and alloys "'k ishigh, While for certain insulating materials such as asbestos, cork and-kapok, k is verylow. Herein heat'conductorswill be considered to have a thermal conductivity constant k .ofas much as about 10 (in the .case .of highly resistant alloys used as heating elements) an'd preferably of as much as about 30; whereas 7 the. ordinary'linsulating materials havelieat conductivity constants k of less than '1 and-usuallyless than 0.1.

.In the electrical arts, electrical conductors are usually understood .tojhave resistivitywhichisdefined as the re- 1 sist ance of a sampletofthe material having both-a length andcross-sectionof.unity. Theresistance of acentimetercube-.and vcireularemil foot .are the two most common units .of;resis.tivity. -Hereim electrical conductors are. un-

derstood .to, have; res istivitie s-, in .michroines per -cm.. r,

not more thanabollt 10D. '(asin thecase. of the .Nichrome? heatingelements) .and preferably not more .thanabout 20; whereas the resistivity of the insulators is usually considered to be at least about 10 ohms per cmfi, and preferably 10 ohms per cmfi.

One synthetic resin which has been used successfully in accordance with the principles of the present invention is molded nylon. The thermal conductivity of the nylon material utilized in the construction of the actuating memher 46 has a thermal conductivity of 5.25.8 (measured in terms of 10* calories per second per square centimeter per 1 C. per centimeter). The volume resistivity of the nylon material utilized is in the range of 4.5 lO -4 10 (measured in terms of ohm-cm. with 50% relative humidity and 23 C.)

Although various minor structural modifications might be suggested by those versed in the art, it should be understood that I wish to embrace within the scope of the patent warranted hereon all such modifications as reasonably and properly come Within the scope of my contribution to the art.

1 claim as my invention:

1. A rheostat switch assembly comprising, a ceramic base plate having a plurality of circumferentially spaced longitudinally extending through holes formed therein, an arcuate groove formed in one face of said plate in register with said through holes, an arcuate complementary shaped resistance coil received in said grooves and supported by said base plate, a contact terminal plate carried by said base plate, said resistance coil being ventilated by air flowing through said base plate at said through holes, a rotatable bridging plate having terminal portions engaging said coil and said contact plate and actuating means for adjustably rotating said bridging plate relative to said base plate, said actuating means consisting of a one-piece member made of electrically and thermally nonconductive material and providing an enlarged bridging plate carrying portion and a shaft portion integral therewith and extending longitudinally away therefrom, said ceramic base having a housing connected thereto providing a bearing portion for journaling said shaft and confining said enlarged bridging plate carrying portion, a continuous biasing spring between said bridging plate carrying portion and said bridging plate loading said bridging plate against said resistance coil and said contact plate, circuit means to be controlled by said rheostat switch assembly including contact terminal means connected to said resistance coil and said contact plate, and a manual actuating knob carried on the free end of said shaft portion.

2. A rheostat switch construction comprising a sheetform housing member bent to provide a longitudinally flanged radially extending centrally apertured wall having a plurality of longitudinally extending circumferentially spaced tongues on the outer periphery thereof, a base assembly longitudinally spaced from said radially extending wall and having :a plurality of recesses corresponding in number and circumferential spacing to said tongues, the end of said tongues being bent over and received in said recesses to connect said base assembly to said housing member, thereby to form a housing enclosure, a generally tubular stern member having one end received in and connected to said centrally apertured radially extending wall and providing a longitudinally extending bore forming a metallic bearing surface, the outer periphery of said stem member being threaded, contact terminal means on said base assembly including a resistance coil, said base assembly having a row of ventilating apertures extending therethrough in register with said resistance coil, a rotatable switch actuator member inside of said hous- Eng enclosure bridging said contact terminal means and said resistance coil, and a one-piece plastic shaft having low thermal conductivity and being electrically insulative, said shaft having an enlarged carrier portion forming one end thereof confined in said housing enclosure to mount said switch actuator member and to retain said shaft in assembly within said housing enclosure, said shaft further including a reduced shaft actuating portion projecting out of said housing enclosure through said centrally apertured wall through said stem member, said actuating portion having a peripheral surface journaled for rotation by said metallic bearing surface, said shaft having means formed at the actuating portion end thereof to receive a manually manipulable actuating knob electrically and thermally insulated from the contact terminal means.

3. A rheostat switch construction comprising a housing having a generally cylindrical neck providing a metallic bearing surface, a shaft member made of plastic material and havin a reduced diameter rod-like actuating portion extending axially outwardly through said neck, said actuating portion having a peripheral journaling surface journaled for rotation by said bearing surface, an integral enlarged carrier portion forming one end of said shaft member and being confined inside of said housing to retain said shaft member and assembly with said housing, switch means in said housing including a rotatable switch actuator member carried on said enlarged carrier port-ion of said shaft member, the actuating portion of said shaft extending axially outwardly of said neck into a manually engageable position for actuation of said switch construction and being electrically and thermally insulated from said switch means by said plastic material, said switch means further including an apertured ceramic base plate having a resistance coil carried thereby in register with said apertures for ventilation thereof and engaged by said actuator member.

References fired in the file of this patent UNITED STATES PATENTS 2,172,397 Meuer Sept. 12, 1939 2,479,557 Chanowitz Aug. 23, 1949 2,536,181 Hultgren Ian. 2, 1951 2,629,789 Benander Feb. 24, 1953 2,645,685 Nefi July 14, 1953 2,685,624 Chermendy et a1 Aug. 3, 1954 2,691,087 Holleran Oct. 5, 1954 

